<!DOCTYPE html>
<html>
  <head>
    <title>Button test</title>
  </head>
  <body>
    <script src="mouse-helper.js"></script>
    <button>Click target</button>
    <script>
      window.result = 'Was not clicked';
      window.offsetX = undefined;
      window.offsetY = undefined;
      window.pageX = undefined;
      window.pageY = undefined;
      window.shiftKey = undefined;
      window.pageX = undefined;
      window.pageY = undefined;
      window.bubbles = undefined;
      document.querySelector('button').addEventListener('click', e => {
        result = 'Clicked';
        offsetX = e.offsetX;
        offsetY = e.offsetY;
        pageX = e.pageX;
        pageY = e.pageY;
        shiftKey = e.shiftKey;
        bubbles = e.bubbles;
        cancelable = e.cancelable;
        composed = e.composed;
      }, false);
    </script>
  </body>
</html>